Re: [PATCH] mm: mark async iocb read as NOWAIT once some data has been, copied

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Sat, Oct 17, 2020 at 09:30:59AM -0600, Jens Axboe wrote:
> Once we've copied some data for an iocb that is marked with IOCB_WAITQ,
> we should no longer attempt to async lock a new page. Instead make sure
> we return the copied amount, and let the caller retry, instead of
> returning -EIOCBQUEUED for a new page.
> 
> This should only be possible with read-ahead disabled on the below
> device, and multiple threads racing on the same file. Haven't been able
> to reproduce on anything else.

Wouldn't this do the job just as well?

@@ -2211,6 +2211,8 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
 
                put_page(page);
                written += ret;
+               if (iocb->ki_flags & IOCB_WAITQ)
+                       iocb->ki_flags |= IOCB_NOWAIT;
                if (!iov_iter_count(iter))
                        goto out;
                if (ret < nr) {